Excited-State Dynamics and Nonlinear Optical Properties of Hyperpolarizable Chromophores Based on Conjugated Bis(terpyridyl)Ru(II) and Palladium and Platinum Porphyrinic Components: Impact of Heavy Metals upon Supermolecular Electro-Optic Properties

Abstract

A new series of strongly coupled oscillators based upon (porphinato)Pd, (porphinato)Pt, and bis(terpyridyl)ruthenium(II) building blocks is described. These RuPPd, RuPPt, RuPPdRu, and RuPPtRu chromophores feature bis(terpyridyl)Ru(II) moieties connected to the (porphinato)metal unit via an ethyne linker that bridges the 4'-terpyridyl and porphyrin macrocycle meso-carbon positions. Pump-probe transient optical data demonstrate sub-picosecond excited singlet-totriplet-state relaxation. The relaxed lowest-energy triplet (T-1) excited states of these chromophores feature absorption manifolds that span the 800-1200 nm spectral region, microsecond triplet-state lifetimes, and large absorptive extinction coefficients [epsilon(T-1 -> T-n) > 4 x 10(4) M-1 cm(-1)]. Dynamic hyperpolarizability (beta(lambda)) values were determined from hyper-Rayleigh light scattering (HRS) measurements carried out at several incident irradiation wavelengths over the 800-1500 nm spectral region. Relative to benchmark RuPZn and RuPZnRu chromophores which showed large beta(HRS) values over the 1200-1600 nm range, RuPPd, RuPPt, RuPPdRu, and RuPPtRu displayed large beta(HRS) values over the 850-1200 nm region. Generalized Thomas-Kuhn sum (TKS) rules and experimental hyperpolarizability values were utilized to determine excited state-to-excited state transition dipole terms from experimental electronic absorption data and thus assessed frequency-dependent beta(lambda) values, including two- and three-level contributions for both beta(zzz) and beta(xzx) tensor components to the RuPPd, RuPPt, RuPPdRu, and RuPPtRu hyperpolarizability spectra. These analyses qualitatively rationalize how the beta(zzz) and beta(xzx) tensor elements influence the observed irradiation wavelength-dependent hyperpolarizability magnitudes. The TKS analysis suggests that supermolecules related to RuPPd, RuPPt, RuPPdRu, and RuPPtRu will likely feature intricate dependences of experimentally determined beta(HRS) values as a function of irradiation wavelength that derive from substantial singlet-triplet mixing, and complex interactions among multiple different beta tensor components that modulate the long wavelength regime of the nonlinear optical response.